| 摘要 |
PURPOSE:To prevent the deterioration in the quality of a read picture by using a binarized threshold value set by a picture density so as to binarize the output signal, counting it and discriminating the adequacy of the threshold value so as to control the threshold value. CONSTITUTION:An input picture signal 6 is compared with a slice level (threshold value) 7 by a comparator 1 and outputs a binarized signal 8. A binary signal counter 2 counts a count number 9 and inputs it to comparators 3, 4. The comparators 3, 4 compare the proper counts C1, C2 (C1<C2) with the count 9, the comparator 3 outputs a signal X1 when the count 9 is larger than the proper count C1 and the comparator 4 outputs a signal X2 when the count 9 is smaller than the proper count C2. With the signals X1, X2 at an H level, an AND 5 outputs a picture density proper signal. When no output is obtained from the AND 5, the slice level 7 is controlled. Thus, white or black level packing of the picture is prevented and the deterioration of picture is prevented.
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